This disclosure relates to a centrifugal refrigerant compressor with a magnetic bearing assembly. More particularly, the disclosure relates to such a refrigerant compressor having a variable geometry diffuser.
Refrigerant compressors are used to circulate refrigerant to a chiller via a refrigerant loop. One type of typical refrigerant compressor operates with a set of variable inlet guide vanes arranged upstream from the impeller for capacity control. The variable inlet guide vanes are actuated during operation of the refrigerant compressor to regulate its capacity during various operating conditions. In one example, the impeller is supported on a rotor shaft by magnetic bearings. Vibrations detected by the magnetic bearing control systems have been used to detect instability in the fluid caused by stall and surge conditions and then regulate the flow through the impeller by controlling the inlet guide vane position.
Variable Geometry Diffusers (VGD) have been suggested for centrifugal refrigerant compressor systems. One typical approach of detecting impeller instability measures the pressure with pressure sensors at either side of the impeller. An undesired pressure differential at a given operating condition indicates impeller instability. The VGD position is then manipulated to regain impeller stability.